1. Field of the Invention
The present invention relates generally to a method and system for controlling and correcting engine ignition timing such that engine ignition timing is controlled and corrected according to the presence or absence of engine knocking, and more particularly to a method and system for detecting engine knocking such that the presence of absence of engine knocking is determined by reference to the rate of change of engine speed.
2. Description of the Prior Art
In order to improve engine performance and fuel consumption efficiency, methods are known for increasing the engine compression ratio and for advancing the ignition timing. However since these methods tend to generate engine knocking, it is necessary to take measures to detect such knocking so that the engine ignition can be delayed to counteract the knocking.
There exist two methods of detecting engine knocking; the first method entails measuring the pressure in the engine cylinders and using the result to correct the ignition timing, the second method entails measuring engine vibrations and using the result to control the ignition timing.
In the former method, when no engine knocking occurs, pressure in the engine cylinders changes smoothly with respect to the crankshaft angle, as depicted by the solid line in FIG. 1; however, when knocking occurs, the pressure changes abruptly because of abnormal fuel combustion, as is depicted by the broken line in FIG. 1. Therefore, it is possible to detect the presence or absence of engine knocking by measuring changes in cylinder pressure. In the vibration measuring method, it is possible to detect the presence or absence of knocking by measuring abnormal engine vibrations caused by the above-mentioned abrupt changes in cylinder pressure.
These prior-art methods for detecting knocking, suffer from a shortcoming in that the cost is relatively high since a high quality pressure sensor which can withstand the high temperatures and pressures of an engine cylinder, or a highly sensitive vibration sensor which can detect small engine vibrations accurately is required. In addition, in connection with the pressure detection method, it is quite difficult to assure the durability of the pressure sensor; and in connection with the vibration detection method, it is difficult to assure the durability of the vibration sensor since a large deformation of the vibrator is required to increase the level of signals detected by the vibration sensor for more accurate detection of engine vibration.
Therefore, prior to the present invention, difficulties have been encountered with regard to efforts to correct the ignition timing of an engine without generating engine knocking.